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Asian Lady Beetle - An Invasion!

There are around 18 species of ladybird beetles in Ontario, all of which feed on aphids and mealy bugs. However, Harmonia axyridis was considered very effective in eradicating the pest problems associated with crops such as soya. Hence it was introduced into USA and thus entered Canada. Here is an account entailing general information and observations on this beetle.

Asian Lady Beetle showing the "W" mark on it's pronotum

Asian Lady Beetle is a beautiful ladybird native to eastern Asia. It is easily identified by the “M” or “W” mark – whichever way you see it, on the pronotum (just behind the head). It lives for one to three years, depending on the availability of food and surviving winter several times. When disturbed – or handled – it produces an odor to deter predators, the smell is however insignificant and can be easily washed away. They are gentle and do not bite to humans, but some people are allergic to this beetle.

It was first introduced in USA in the year 1916 to control the pest population of aphids, and after consecutive efforts, it became acclimatized to the area. Thence it ever spread farther, and reached Canada. It is now abundant than the native Ladybird beetles seen around. In Europe as well, the species spread quickly and almost replaced native ladybirds of Britain.

Photographed at south shore of Lake Huron during Summer

This is one of the rather skeptical cases of introducing an exotic species to control the pest population in a certain country. There are failed instance which includes introduction of Cane Toad in Australia, to control the beetle grubs that damaged sugarcane. However, the toad developed taste for the native beetles, and soon became an invasive species. This resulted in a decline in the native insect biodiversity along with receding reptile population due to competition for food.

There are several successful cases of biological control of pest population by exotic species. One of the cases is, in which the cottony cushion scale insect – a pest on citrus trees, was the reason for major loss of the Californian citrus industry. A vedalia beetle and a parasitoid fly were then introduced from Australia to control the pest population. After a few years, the pest was completely controlled by these exotic predators. And the availability of food, in this case, the scale insect, determined the population density of the exotic predator, thus controlling its invasiveness.

Aphids are hemiptera bugs, feeding on plant sap.
They reproduce extremely rapidly and thus expand and
exploit the food sources available, including crops. Photographed in India.

However, not all such cases are like these. In case of Harmonia axyridis, the beetle was successful in eliminating aphids – a farmer and a gardener’s nightmare. So long as the beetle consumed the aphids, all was okay. But it spread rapidly all over the place, and replaced the native populations of ladybirds – through competition for food. This resulted in a loss of native biodiversity, and that is not good! Also, it is known to damage crops such as grapes.

“Adults feed on grapes in the late fall for sugars to survive during hibernation. However, they get harvested along with the grapes. When crushed with the grapes they impart a musty odor to juice or wine. The odor is because of a compound called methoxypyrazine, which is a stable compound and resistant to heat, fermentation and filtering. ” Timothy E. Martinson et al, The Buzz on Asian Lady Beetles

Albeit these facts, this beetle is still considered a blessing by a farmer – thanks to its gregarious appetite for aphids.

Different morphs

All Ladybird beetles hibernate during winter season. And so, the best time to see them – in their thousands – is during autumn. This is the time when, all of a sudden, they come and land on trees and buildings. They make it into your homes, and are a menace. But they don’t mean to. They are actually seeking shelter from the coming of cold. Therefore, they seek the corners and warm places so as to survive the winter.

“Houses – particularly light colored ones – look like rock faced cliffs to lady beetles in the fall. This has been a minor problem in Central NY since the mid 90s.” Timothy E. Martinson et al, The Buzz on Asian Lady Beetles

Five different morphs as seen during the invasion

Now, you may come across a myriad of colors from orange to red and melanistic forms, and patterns (such as no spots, less spots, dark spots, so on) on these lady beetles marked with an "M" on the pronotum, and thus around fifteen morphs - or more, exist today, out of which, I recorded only five in London ON. These morphs are a result of genetic variation.

In nature the lady beetles shelter in tree crevices, under rocks and in leaf litter. But unfortunately, they land up on big structures like high rise buildings – mistaking them to be trees, and seek shelter in apartments. But worry not, it’s a pleasurable company!

Two sleepy beetles at my home

According to my observations, many of these beetles that made into my house died after two weeks. And the ones that were all over the place outside, vanished. I think the death was because of being active throughout the time – thanks to the constant warmth provided by my heater but, no food source. The rest of those who vanished must have sought a protective shelter and slept calmly.

So, after a long winter sleep, the ladybirds rise up and go on a search for mates. This happens during spring time. That’s the time when they congregate again and invade homes – actually, to seek shelter for mating. Thus be the life of these beautiful, yet invasive Ladybirds – Harmonia axyridis.